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-rw-r--r--arch/x86_64/kernel/semaphore.c180
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diff --git a/arch/x86_64/kernel/semaphore.c b/arch/x86_64/kernel/semaphore.c
deleted file mode 100644
index 48f7c18172b9..000000000000
--- a/arch/x86_64/kernel/semaphore.c
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1/*
2 * x86_64 semaphore implementation.
3 *
4 * (C) Copyright 1999 Linus Torvalds
5 *
6 * Portions Copyright 1999 Red Hat, Inc.
7 *
8 * This program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License
10 * as published by the Free Software Foundation; either version
11 * 2 of the License, or (at your option) any later version.
12 *
13 * rw semaphores implemented November 1999 by Benjamin LaHaise <bcrl@kvack.org>
14 */
15#include <linux/config.h>
16#include <linux/sched.h>
17#include <linux/init.h>
18#include <asm/errno.h>
19
20#include <asm/semaphore.h>
21
22/*
23 * Semaphores are implemented using a two-way counter:
24 * The "count" variable is decremented for each process
25 * that tries to acquire the semaphore, while the "sleeping"
26 * variable is a count of such acquires.
27 *
28 * Notably, the inline "up()" and "down()" functions can
29 * efficiently test if they need to do any extra work (up
30 * needs to do something only if count was negative before
31 * the increment operation.
32 *
33 * "sleeping" and the contention routine ordering is protected
34 * by the spinlock in the semaphore's waitqueue head.
35 *
36 * Note that these functions are only called when there is
37 * contention on the lock, and as such all this is the
38 * "non-critical" part of the whole semaphore business. The
39 * critical part is the inline stuff in <asm/semaphore.h>
40 * where we want to avoid any extra jumps and calls.
41 */
42
43/*
44 * Logic:
45 * - only on a boundary condition do we need to care. When we go
46 * from a negative count to a non-negative, we wake people up.
47 * - when we go from a non-negative count to a negative do we
48 * (a) synchronize with the "sleeper" count and (b) make sure
49 * that we're on the wakeup list before we synchronize so that
50 * we cannot lose wakeup events.
51 */
52
53void __up(struct semaphore *sem)
54{
55 wake_up(&sem->wait);
56}
57
58void __sched __down(struct semaphore * sem)
59{
60 struct task_struct *tsk = current;
61 DECLARE_WAITQUEUE(wait, tsk);
62 unsigned long flags;
63
64 tsk->state = TASK_UNINTERRUPTIBLE;
65 spin_lock_irqsave(&sem->wait.lock, flags);
66 add_wait_queue_exclusive_locked(&sem->wait, &wait);
67
68 sem->sleepers++;
69 for (;;) {
70 int sleepers = sem->sleepers;
71
72 /*
73 * Add "everybody else" into it. They aren't
74 * playing, because we own the spinlock in
75 * the wait_queue_head.
76 */
77 if (!atomic_add_negative(sleepers - 1, &sem->count)) {
78 sem->sleepers = 0;
79 break;
80 }
81 sem->sleepers = 1; /* us - see -1 above */
82 spin_unlock_irqrestore(&sem->wait.lock, flags);
83
84 schedule();
85
86 spin_lock_irqsave(&sem->wait.lock, flags);
87 tsk->state = TASK_UNINTERRUPTIBLE;
88 }
89 remove_wait_queue_locked(&sem->wait, &wait);
90 wake_up_locked(&sem->wait);
91 spin_unlock_irqrestore(&sem->wait.lock, flags);
92 tsk->state = TASK_RUNNING;
93}
94
95int __sched __down_interruptible(struct semaphore * sem)
96{
97 int retval = 0;
98 struct task_struct *tsk = current;
99 DECLARE_WAITQUEUE(wait, tsk);
100 unsigned long flags;
101
102 tsk->state = TASK_INTERRUPTIBLE;
103 spin_lock_irqsave(&sem->wait.lock, flags);
104 add_wait_queue_exclusive_locked(&sem->wait, &wait);
105
106 sem->sleepers++;
107 for (;;) {
108 int sleepers = sem->sleepers;
109
110 /*
111 * With signals pending, this turns into
112 * the trylock failure case - we won't be
113 * sleeping, and we* can't get the lock as
114 * it has contention. Just correct the count
115 * and exit.
116 */
117 if (signal_pending(current)) {
118 retval = -EINTR;
119 sem->sleepers = 0;
120 atomic_add(sleepers, &sem->count);
121 break;
122 }
123
124 /*
125 * Add "everybody else" into it. They aren't
126 * playing, because we own the spinlock in
127 * wait_queue_head. The "-1" is because we're
128 * still hoping to get the semaphore.
129 */
130 if (!atomic_add_negative(sleepers - 1, &sem->count)) {
131 sem->sleepers = 0;
132 break;
133 }
134 sem->sleepers = 1; /* us - see -1 above */
135 spin_unlock_irqrestore(&sem->wait.lock, flags);
136
137 schedule();
138
139 spin_lock_irqsave(&sem->wait.lock, flags);
140 tsk->state = TASK_INTERRUPTIBLE;
141 }
142 remove_wait_queue_locked(&sem->wait, &wait);
143 wake_up_locked(&sem->wait);
144 spin_unlock_irqrestore(&sem->wait.lock, flags);
145
146 tsk->state = TASK_RUNNING;
147 return retval;
148}
149
150/*
151 * Trylock failed - make sure we correct for
152 * having decremented the count.
153 *
154 * We could have done the trylock with a
155 * single "cmpxchg" without failure cases,
156 * but then it wouldn't work on a 386.
157 */
158int __down_trylock(struct semaphore * sem)
159{
160 int sleepers;
161 unsigned long flags;
162
163 spin_lock_irqsave(&sem->wait.lock, flags);
164 sleepers = sem->sleepers + 1;
165 sem->sleepers = 0;
166
167 /*
168 * Add "everybody else" and us into it. They aren't
169 * playing, because we own the spinlock in the
170 * wait_queue_head.
171 */
172 if (!atomic_add_negative(sleepers, &sem->count)) {
173 wake_up_locked(&sem->wait);
174 }
175
176 spin_unlock_irqrestore(&sem->wait.lock, flags);
177 return 1;
178}
179
180
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